Optimizer: Replace the MandatoryCombine pass with a Simplification pass, which is implemented in Swift

The Swift Simplification pass can do more than the old MandatoryCombine pass: simplification of more instruction types and dead code elimination.
The result is a better -Onone performance while still keeping debug info consistent.

Currently following code patterns are simplified:
* `struct` -> `struct_extract`
* `enum` -> `unchecked_enum_data`
* `partial_apply` -> `apply`
* `br` to a 1:1 related block
* `cond_br` with a constant condition
* `isConcrete` and `is_same_metadata` builtins

More simplifications can be added in the future.

rdar://96708429
rdar://104562580

Author: eeckstein

include/swift/SILOptimizer/PassManager/Passes.def

@@ -434,10 +434,6 @@ PASS(YieldOnceCheck, "yield-once-check",
 PASS(OSLogOptimization, "os-log-optimization", "Optimize os log calls")
 PASS(ForEachLoopUnroll, "for-each-loop-unroll",
      "Unroll forEach loops over array literals")
-PASS(MandatoryCombine, "mandatory-combine",
-    "Perform mandatory peephole combines")
-PASS(OptimizedMandatoryCombine, "optimized-mandatory-combine",
-    "Perform -O level mandatory peephole combines")
 PASS(BugReducerTester, "bug-reducer-tester",
      "sil-bug-reducer Tool Testing by Asserting on a Sentinel Function")
 PASS(AssemblyVisionRemarkGenerator, "assembly-vision-remark-generator",

lib/SILOptimizer/Mandatory/CMakeLists.txt

@@ -38,7 +38,6 @@ target_sources(swiftSILOptimizer PRIVATE
   RawSILInstLowering.cpp
   SILGenCleanup.cpp
   YieldOnceCheck.cpp
-  MandatoryCombine.cpp
   OSLogOptimization.cpp
   MoveOnlyWrappedTypeEliminator.cpp
   OwnershipModelEliminator.cpp)